Compounds having the structural formula ##STR3## wherein X can be alkyl, n can be 0, 1, or 2, and R.sub.1 can be phenyl or substituted phenyl are described in Japanese Patent Application 84632-1974 as being intermediates for the preparation of herbicidal compounds of the formula ##STR4## wherein R.sub.1, X, and n are as defined above and R.sub.2 is alkyl, alkenyl, or alkynyl. Specifically taught herbicidal compounds of this latter group are those where n is 2, X is 5,5-dimethyl, R.sub.2 is allyl and R.sub.1 is phenyl, 4-chlorophenyl or 4-methoyxphenyl.
The precursor intermediates for these three specifically taught compounds have no or almost no herbicidal activity.
European Patent Application No. 83 102 599.4 was published October 5, 1983 and relates to certain novel 2-(2-substituted benzoyl)-cyclohexane-1,3-diones as herbicides. The compounds have the following structural formula ##STR5## wherein R and R.sup.1 are hydrogen or C.sub.1 -C.sub.4 alkyl; R.sup.2 is chlorine, bromine, or iodine; R.sup.3 is hydrogen or halogen; and R.sup.4 is hydrogen, chlorine, bromine, iodine, C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy, nitro or trifluoromethyl.
In contrast to the teaching of the cited Japanese patent application, the compounds of this invention have exceptional herbicidal activity. Applicant's compounds must have the recited substitution in the 2-position of the phenyl moiety of their compounds to obtain the exceptional herbicidal activity. The exact reason why this substitution imparts exceptional herbicidal activity to the compounds is not fully understood.